This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | -1 |
| 3 | -3 |
| 4 | -3 |
| 5 | 5 |
| 6 | 15 |
| 7 | -21 |
| 8 | -133 |
| 9 | 27 |
| 10 | 1215 |
| 11 | 935 |
| 12 | -12441 |
| 13 | -23673 |
| 14 | 138047 |
| 15 | 469455 |
| 16 | -1601265 |
| 17 | -9112561 |
| 18 | 18108927 |
| 19 | 182135007 |
| 20 | -161934625 |
| 21 | -3804634785 |
| 22 | -404007681 |
| 23 | 83297957567 |